Figure 1. Microdochium patch in Poa annua green.
Figure 2. Microdochium patch - note movement of spores tracked on mower.
The lingering spring weather pattern of cool, wet, cloudy…conditions is ideal for the occurrence of Microdochium patch, which is Pink Snow Mold without the snow cover, caused by the fungus (Microdochium nivale). With the recent cold fronts and rainfall, cases have been reported in both central Ohio and N. E. Ohio. It server damage is now present on turf (mainly Poa annua / greens) the injury may be difficult to recover from until there is prolonged warm and dry weather conditions. The photos are from late April 2013. In most years there are cases confirmed of this disease as late as June. The problem with this disease is that it can be confused and misdiagnosed as cool temperature pythium in the spring. Rarely do we see cool temperature pythium in Ohio. Microdochium patch is especially active on annual bluegrass in areas that are, in shade, wet, north facing, or have a history of the disease. Creeping bentgrass is also susceptible to pink snow mold but not to the same extent as annual bluegrass. Another common name used for this disease in the past is Fusarium patch.
In late spring when temperatures are between 40˚ and 60˚ F and abundant moisture is present, the pathogen becomes quit active. The pathogen produces abundant spores that move in water along drainage patterns and can easily be tracked by mowers. In spring symptoms are more variable and may appear as streaks. Symptoms initially appear as a yellowing of the infected turf area then progresses rapidly to a rusty, reddish, brown color (Fig 1.). The source of spores is often from old patches (Fig 2.). When the disease occurs in late spring it is usually active for short periods of time so the patches are not as large, distinct, or well defined as in winter and makes diagnosis more difficult. With the return of warm and dry weather the turf will often recover rapidly.
Cultural management of pink snow mold includes mowing greens, if possible, when they are dry; and improved drainage. Often these are limited things you can do since the weather is out of your control and is the major factor for disease development.
Fungicide treatments can be effective for controlling pink snow mold. Many products are labeled, some that are used include Iprodione, Iprodione + Chlorothalonil, Fludioxonil, Thiophanate-methyl, Myclobutanil, Triademefon, Propiconazole, Azoxystrobin, Trifloxystrobin, Pyraclostrobin, and other labeled fungicides.
If you would like verification of this disease you can submit a sample to the Ohio State University Plant Diagnostic Clinic.
C. Wayne Ellett Plant and Pest Diagnostic Clinic
201 Kottman Hall
2021 Coffey Road
Columbus, Ohio 43210